The present invention relates to a rolling element chain of the type including a plurality of rolling elements arranged in close succession, a longitudinal supporting band having a plurality of recesses for the accommodation of the rolling elements, a plurality of retaining elements for retaining the rolling elements accommodated in the recesses, each rolling element being assigned at least one retaining element, and at least one longitudinal flexible element for interconnecting the retaining elements.
A rolling element chain of this kind is disclosed in, for example, DE 198 24 250 A1.
Japanese Letters of Disclosure 5-52217 (1993) for Japanese Patent Application 3-235563 (1991) disclose a rolling element chain, which comprises a plurality of balls that are arranged in recesses of a supporting band. A retaining element having, at each of its leading and following sides in the longitudinal direction of the supporting band, a retaining surface for sliding engagement with the leading or following ball is arranged between two successive balls in each instance. The retaining elements are interconnected by means of two flexible strip elements and together therewith form the supporting band.
This known ball-bearing chain has the advantage that the balls may be arranged in close succession, i.e., at a short distance apart. In such case, the ratio of the ball diameter to the distance between the midpoints of two adjacent balls is approximately 1:1. Because of the resultant high ball density, the known ball-bearing chain has a high loading or carrying capacity. However, stiffening of the supporting band, which goes hand in hand with fastening of the two strip elements to the retaining elements in the region between two successive balls, is disadvantageous. The strip elements of the supporting band are able to react to bending of the supporting band about an axis running parallel to the transverse direction of the band, for example in the turn-around sections of the raceway of a linear bearing, only in the region of the lateral contact of the band with the balls, but not in the region of its lateral fastening to the retaining elements.
The consequent relatively high bending of the supporting band in the region of its lateral contact with the balls results in a corresponding restoring force of the band in its straight-line position, resulting from the elasticity of the material of the supporting band. Because of the retaining engagement of the supporting band with the balls, this restoring force influences the motion of the balls in the turn-around sections of the raceway. In a linear bearing provided with the known rolling element chain, high bending of the supporting band may result in the pronounced development of noise, in increased friction of the strip elements in the guide grooves, and in deterioration in fatigue strength because of high bending stress.
Other ball-bearing chains with balls in close succession are disclosed, for example, in U.S. Pat. No. 2,897,021 and U.S. Pat. No. 3,292,981. In these chains, too, a retaining element that has a retaining surface for sliding engagement with the preceding ball as well as a retaining surface for sliding engagement with the following ball bearing is arranged between two successive balls in each instance.
Another non-generic rolling element chain is disclosed in Japanese Letters of Disclosure 62-242126 (1987) for Japanese Patent Application 60-253865 (1985). In the rolling element chain disclosed in FIGS. 5 and 6 thereof, each rolling element is retained by two retaining elements assigned to it and to it only. Thus, two physically separate retaining elements, which are arranged in a central section of the supporting band at a specific distance apart, are provided between two successive rolling elements.
The supporting band of this known rolling element chain has the advantage that it can be bent about an axis running parallel to the transverse direction not only in the regions of its lateral contact with the rolling elements, but in the regions between two successive rolling elements as well. Owing to twice the number of bending points as compared with JP-A-5-52217 (1993), at a like curvature of a turn-around section of the raceway the supporting band is bent less at each individual bending point and influences travel of the rolling elements to a correspondingly lesser extent, which results in quieter operation of a linear bearing provided with this rolling element chain. However, the rolling element chain disclosed in JP-A-62-242126 (1987) has the disadvantage that the rolling elements are arranged in loose succession, i.e., at a relatively greater distance apart, in order to be able to provide the required space for the separate retaining elements. In that chain, the ratio of the ball diameter to the distance between the midpoints of two adjacent balls is about 1:1.5. The resulting lower density of rolling elements is attended by a corresponding decrease in loading capacity of the rolling element chain.
German Patent 835 718 discloses a rolling element chain in which the distance between successive rolling elements is about twice the diameter of the rolling elements. The rolling elements are retained by tongues, which are arranged between them, of a spring steel band carrying them. A rolling element chain with a similar distance between rolling elements, i.e., a similar loose succession of rolling elements, is disclosed in U.S. Pat. No. 2,557,476.
DE 36 35 261 A1 describes a ball-bearing chain of moderate spacing apart of the balls, i.e., the ratio of the ball diameter to the distance between the midpoints of successive balls is about 1:1.25. Each of the balls is assigned retaining elements, separated from one another, which are arranged between the balls. The retaining elements therefore are very small and can hardly provide the balls with any retention.
The ball chain disclosed in DE 29 06 128 A1 is made of a number of chain units designed independent of one another, each of which serves for the guidance of only one of the balls. This arrangement results in a loose succession of balls in which the apertures accommodating the balls provide no retention for the balls. The chain units, therefore, additionally have guide blocks, separated from the accommodation apertures, which center the chain units in the ball-bearing raceway and especially the turn-around sections with regard to travel of the balls.
In addition, reference is made to DE 37 09 039 C2, DE 89 14 085 U and U.S. Pat. No. 2,566,421.
DE 198 24 250 A1, mentioned above, improved the quietness of operation of the known chains of rolling elements discussed above by increasing the number of possible bending points of the supporting band.
In contrast, the object of the present invention is to allow the rolling element chains to become even more flexible without losing loading or carrying capacity.
According to the invention, the foregoing object is attained by a rolling element chain that comprises a plurality of rolling elements arranged in close succession and a longitudinal supporting band having a plurality of recesses for accommodation of the rolling elements. The supporting band has a plurality of retaining elements for retention of the rolling elements accommodated in the recesses, with each rolling element being assigned at least one retaining element. The supporting band further comprises at least one longitudinal flexible element for interconnection of the retaining elements, while in addition each rolling element is retained, by the at least one retaining element assigned to it, in the longitudinal direction of the supporting band either at its leading side only or at its following side only. In other words, when at least some of the rolling elements are assigned a plurality of retaining elements, the retaining elements assigned to one and the same rolling element are arranged, viewed in the longitudinal direction of the supporting band, either all before this rolling element or all after this rolling element. According to the invention, therefore, each rolling element is secured at one longitudinal side only by the retaining element(s) assigned to it in the associated recess.
Owing to the reduction, according to the invention, of the regions in which the rolling element chain has retaining elements, extension of the flexible regions of the chain is increased in countermotion. Hence, the flexibility of the chain as a whole is increased. Owing to the reduction in the number of retaining elements, however, the function of the chain in the rolling-element raceway is not impaired. Also, upon both the introduction of the chain provided with rolling elements into the raceway and its removal therefrom, the retaining elements are capable of exerting their retaining function on the rolling elements as long as the supporting band runs straight. In addition, the greater flexibility of the supporting band facilitates the installation of rolling elements.
As has already been indicated above in the discussion of the prior art, according to the invention a close succession of rolling elements is intended to mean a succession in which the ratio of the diameter of the rolling elements to the distance between the midpoints of successive rolling elements is less than 1:1.5, preferably less than 1:1.25, and most preferably approximately 1:1.
The rolling element chain according to the invention, and in particular its supporting band, may be produced in simple fashion. Thus, the band may be made in one piece, for example of a synthetic material of the group of elastomers, such as, for example, polyurethane, hytrel or the like, and preferably as an injection molding.
According to a first variant, the retaining elements assigned to two adjacent rolling elements, and preferably to all rolling elements, may be arranged either all before or all after such rolling elements. According to a second variant, however, it may alternatively be provided that the retaining elements assigned to two adjacent rolling elements are all arranged between the rolling elements. The second variant may alternatively be periodically continued, so that either all retaining elements assigned to the two rolling elements are arranged between two successive rolling elements or no retaining element at all is arranged therebetween. Also, the two variants may alternatively be used intermixed.
In the second variant, in order to be able to prevent impairment of flexibility of the supporting band in the region between successive rolling elements in the case of a small, or, indeed, in the extreme case even a vanishing distance between the retaining elements in the principal plane of the supporting band, the distance between retaining elements assigned to two adjacent successive rolling elements may increase with increasing distance from the principal plane of the supporting band. This prevents the occurrence of contact between adjacent retaining elements that would limit the bending angle, even in the case of small bending angles. At the same time, it is especially advantageous if the distance between the two adjacent retaining elements, in at least one section adjacent to the principal plane of the supporting band, increases monotonically with increasing distance from the principal plane of the supporting band.
The longitudinal supporting band may be designed conductor-like, in which the two lateral edge sections of the supporting band in each instance have a spar element, which spar elements are connected together by sprocket elements running in substantially the transverse direction of the supporting band. In a supporting band designed in this way, the retaining elements may be arranged on the sprocket elements. However, they may alternatively be arranged on the spar elements or alternatively on the sprocket elements as well as on the spar elements.
In accordance with the invention, at least one sprocket element may be designed as a double sprocket element, i.e., be divided into two partial sprocket elements by a slot running transverse to the direction of travel. At the same time, two partial sprocket elements forming a double sprocket element may be connected, separated from one another, with a spar element. Such connection may alternatively be made via a common crosspiece. In order to minimize the effect on the flexibility of the supporting band, it is additionally proposed that this crosspiece be tapered toward the spar element.
The at least one retaining element assigned to each rolling element preferably projects below and/or above the principal plane of the supporting band. This provides a retaining surface extending over a great angular range, which ensures secure retention of the rolling element. The possible angular range is limited only in that the retaining elements should not drag on a bearing surface of the rolling elements, particularly at a turn-around section of the raceway of the supporting band.
Especially secure retention of a rolling element can be obtained when the rolling element is retained, on the one hand, by as great as possible a portion of the peripheral surface of the recess accommodating the rolling element and, on the other, by a plurality of retaining elements. Preferably, the retaining elements may in addition have a contact or retaining surface that is adapted to the outer contour of the rolling element.
A retaining element may, for example, be cylindrically shaped, and a cylindrical cover surface thereof turned toward a rolling element may assume the function of a contact or retaining surface. When the retaining element is assigned to a spherical rolling element, a spherical-concave shape of the cover surface is advantageous. In addition, the axis of a retaining element designed in this way may lie parallel to the longitudinal direction of the guide band. A retaining element designed in this way preferably is arranged in the central section of the guide band.
The retaining elements may alternatively be arranged in the edge regions of the guide band, especially when more than one retaining element is assigned to a rolling element. Then, for example, retaining elements may be arranged at both edge sections of the guide band. Such an arrangement is especially advantageous when the rolling elements are balls. In such case, segments of a hollow ball or alternatively sections of a ring may be considered for the form of the retaining elements.
The forms of retaining elements discussed above may be combined with one another and, alternatively, with other possible variants.